The method for drying the ink applied to the substrate is used for drying the ink applied to an epoxy-resin printed-circuit board, for example.
The ink drying method will be described. Areas for performing solder plating (e.g., land, through-hole, pad, and the like) are formed on the epoxy-resin printed-circuit board, and ink is applied in a finishing step of the printed-circuit board on which the areas for performing solder plating are formed.
In a case where ultraviolet curing ink is used as the ink applied to the board surface of the printed-circuit board, first, the ink is applied on the entire surface of the printed-circuit board where a copper leaf wiring is formed. Thereafter, the printed-circuit board on which the ink is applied is set in a preheating chamber and a warm current of air of 80° C. is blown to the ink on the printed-circuit board for 15 minutes.
Next, the copper leaf part of the pattern of the preheated printed-circuit board on which mainly the components are to be loaded is masked, and ultraviolet rays are irradiated to expose the areas other than the copper leaf part. Through the exposure processing, the unmasked areas other than the copper leaf part are exposed, and the ink in that areas is cured.
Next, developing processing is executed by using an alkali aqueous solution. When executing the developing processing, the ink in the unmasked areas other than the copper leaf part is cured by irradiation of the ultraviolet rays and remained on the printed-circuit board without being eliminated. Thus, protection and insulation of the copper leaf pattern other than the copper leaf part on which the components are to be loaded are maintained.
In order to fully cure the ink on the printed-circuit board at last, processing for blowing a warm current of air of 150° C. on the board surface of the printed-circuit board over 60 minutes to 90 minutes is executed.    Patent Document 1: Japanese Patent Application No. 2009-524328 (Re-publication of PCT international Publication)
However, because the processing for blowing a warm current of air of 150° C. on the printed-circuit board over 60 minutes to 90 minutes is executed, a thermal stress is given to the printed-circuit board.
Further, 60 minutes to 90 minutes of time is spent for drying the ink applied to the printed-circuit board, not only the manufacture efficiency becomes poor but also the warm current of air needs to be supplied continuously for 60 minutes to 90 minutes. Thus, it is difficult to save the energy.
OHMICHI Co., ltd that is one of the applicants of the present invention has developed a technique which uses overheated dry vapor for drying printed matters (Patent Document 1: Re-publication of PCT international Publication). This drying method may be employed as the method for drying the ink on the printed-circuit board described above.
The printed matter drying method mentioned above employs the structure which: observes a printed matter by an electron microscope; pays an attention to a fact that the printed matter is of sheet-like structure with the entangling fibers and there are pores opened through the top and back faces of the printed matter between the entangling fibers; and a part of overheated dry vapor is discharged by letting it through the pores. Thereby, an original structure (prevention of wrinkles, heat wrinkles, prevention of blisters) is constituted with which the printed matter retains the moisture content of about 7%.
For retaining the moisture content of about 7% as in the case of the printed matter, the structure of discharging a part of the overheated dry vapor by letting it through the pores is employed. However, in order to dry the ink applied to the printed-circuit board, the moisture content of the printed-circuit board is required to be close to zero as much as possible. Thus, the printed matter drying method cannot be applied directly for drying the ink applied to the printed-circuit board, and it is necessary to develop an original method for drying the ink applied to the printed-circuit board.
For developing the method for drying the ink on a substrate such as a printed-circuit board, it is important to dry the ink in a short time by lightening the thermal stress given to the substrate and the like.
It is an object of the present invention to provide an ink drying method which shortens drying time of ink which is applied to a substrate and lightens the thermal stress given to the substrate and the like to dry the ink not by simply utilizing overheated dry vapor but by modifying the overheated vapor to have optimal characteristics for drying the ink and to provide a device thereof.